Method of etching sic



United States Patent us. c1. 156-17 Int. Cl. Hon 7/62; czar 1/00 3 Claims ABSTRACT OF THE DISCLOSURE Silicon carbide bodies used in the fabrication of semiconductive elements are symmetrically etched by immersion in a hot melt comprising of 1:1 ratio of NaNO and Na O at 400600 C.

This invention relates to a method of etching silicon carbide.

In the fabrication of semiconductor elements, such as diodes, transistors or similar components, extensive use is made of the etching technique since like hardly any other material processing technique it makes possible the processing of small and very small bodies in a simple manner. A particular advantage of this technique resides in the fact that, by using etchants reacting exclusively or preferably with certain given materials, it is possible to effect a zone selection when bodies consisting dilferent substances or masks consisting of suitable substances are employed. For the numerous semiconductor substances that have been disclosed so far and for the various problems arising in processing them, a large variety of etchants and etching techniques have been provided with which it has been possible to obtain optimum results in the individual fields.

However, all of the etchants and etching techniques disclosed so far have proved to be impractical for processing SiC as they effect an asymmetric erosion of the material subjected to the etching process, which is of disadvantage for ,most uses. The said disadvantages occur also in the alkali etching techniques which are particularly well suited for SiC.

In order to avoid the aforementioned disadvantages and to make possible an economic processing of SiC, which is gaining increasing importance in the semiconductor art,

this invention provides a method of etching silicon carbide in which the bodies or surfaces to be etched, after having first been lapped by mechanical means to a roughness of preferably below 1 micron, cleaned by ultrasonic treatment, washed with HFHNO and rinsed with aqua destillata and alcohol, are placed into a melt consisting of Na O and NaNO An especially advantageous temperature range has proved to be that between 400 C. and 600 C. A 1:1 mixture ratio of the said substance has shown to be favorable, but other mixture ratios are also possible which for special applications may in certain circumstances deviate greatly from the 1:1 ratio. The silicon carbide bodies etched by this technique are eroded symmetrically and exhibit perfectly planar surfaces.

We claim: 1. The method of symmetrically etching the surface of a silicon carbide body comprising:

applying to the silicon carbide surface to be etched a melt consisting essentially of sodium peroxide and sodium nitrite; the weight ratio between the sodium peroxide and sodium nitrite being on the order of 1 to 1; and maintaining contact between said surface and said melt until the desired amount of etching has taken place; said melt being maintained during the etching step at a temperature between about 400 C. and 600 C. 2. The method of symmetrically etching the surface of a silicon carbide body comprising:

mechanically smoothing said silicon carbide surface to be etched to a roughness of less than about one micron; applying to said surface a melt consisting essentially of sodium peroxide and sodium nitrite; the weight ratio between the sodium peroxide and sodium nitrite being on the order of 1 to 1; and maintaining contact between said surface and said melt until the desired amount of etching has taken place; said melt being maintained during said etching step at a temperature between about 400 C. and 600 C. 3. The method of symmetrically etching the surface of a silicon carbide body comprising:

mechanically smoothing said silicon carbide surface to be etched to a roughness of less than about one micron; ultrasonically cleaning said surface; washing said surface with a solution of hydrofluoric acid and nitric acid; rinsing said surface; applying to said surface a melt consisting essentially of sodium peroxide and sodium nitrite; the weight ratio between the sodium peroxide and sodium nitrite being on the order of 1 to 1; and

maintaining contact between said surface and said melt until the desired amount of etching has taken place; said melt being maintained during the etching step at a temperature between about 400 C. and 600 C.

References Cited Silicon Carbide, Proceedings of Conf. on Silicon Carbide edited by OConnor et al., pages 407 thru 411 and 415, publ. by Pergamon Press, N.Y., July 22, 1960, copy in Library. TK 78 72 54C 48.

Article on the etching of silicon carbide by Faust.

JACOB H. STEINBERG, Primary Examiner.

US. Cl. X.R. 

